1. Field of the Invention
The field of art to which this invention pertains is hydrocarbon processing. It particularly relates to an improved HF alkylation process in which HF loss is reduced.
2. Prior Art
The importance of higher molecular weight isoparaffins, having valuable antiknock properties, is increasing with the present progressive restrictions upon the lead content of gasoline. A convenient source of such higher molecular weight isoparaffins is the catalytic alkylation of lower boiling isoparaffins, such as isobutane, with olefins such as propene and butenes. Catalytic alkylation using hydrofluoric acid has become an important tool for preparing motor fuel blending components.
Hydrofluoric acid is a hazardous chemical with properties peculiar to itself which call for special handling and treatment. With improper treatment it can be lethal. For this reason processes for its use must be equipped with systems which effectively prevent its escape into the atmosphere. Common practice in the art is to chemically treat HF-containing streams which discharge from alkylation processes.
Treating processes in current use counter-currently contact acidic gases with an aqueous solution of a metal hydroxide, such as potassium hydroxide, within an elaborate plate-type contact tower. Where KOH is used as the metal hydroxide, KF is formed.
The resulting aqueous KF solution is further contacted with Ca(OH).sub.2 to precipitate CaF.sub.2 which is highly insoluble in water. The fluoride precipitate, in the form of a sludge, is then disposed of as waste.
Operators of these prior art processes must replenish the HF lost by chemical treatment of waste gases. The disposal of a precipitate sludge also poses an inconvenience to the processor.
Acidic liquids discharging from prior art HF alkylation processes are commonly passed to a receptacle, such as a pit, where they are contacted with Ca(OH).sub.2 for neutralization. HF in these liquids is not recovered from the precipitated CaF.sub.2 and is, therefore, lost.
HF can be recovered from exiting acidic gases and liquids facilly and economically by the use of our invention. HF loss from the process and the HF replenishment which loss necessitates are thereby greatly reduced. The use of elaborate and inconvenient prior art processes involving the disposal of treatment wastes is also avoided by use of the present invention.